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The Alps: Glaciers, Lakes, and Rivers
The Alpine heights, which rise above the snow line, sustain no fewer than 1,200 glaciers and névé fields of firm granules formed from snowflakes that solidify into ice. The largest glacier is the Aletsch, 16 miles long, which covers an area of approximately 66 square miles. These curious ice rivers, characteristic of lofty mountains as well as the polar regions, were first studied in the Alps, and their slow and complex movements were carefully investigated. Like other glaciers the world over, they seem to be slowly retreating, suggesting a gradual warming of the global climate. But there is some evidence that they increased during the centuries immediately preceding the Christian era, as though the prolonged ebbing of the Ice Age had been interrupted by a period of declining temperatures. In some places they descend to an elevation of 3,200 feet, where they continue to wear down mountain flanks, widen gorgelike valleys, and build up accumulations of detritus (debris resulting from rock disintegration).
The far greater glacial action that occurred during the Ice Age is also everywhere in evidence in the Alps. Many circular basins or cirques have been scoured out by the abrasion of rock fragments gripped by moving ice. Many V-shaped valleys broadened out to the more commodious U formation as mountain flanks were worn away; many sharp crags were sculptured from the larger mountain mass. The landscape has been littered with terminal moraines (accumulations of earth and stone deposited by a glacier when the ice was at its maximum extent).
Other relics of the Ice Age are the Alpine lakes, which are noted for their scenic beauty. Those that fan out into Italian territory from the southern border, such as Maggiore and Como, are popular tourist resorts, but others in the heart of the mountainous area, such as Geneva, Lucerne, and Constance, are equally lovely.
Since these lakes usually fill gorges that have been deepened or dammed up by glacial action, they are often very deep. Thus Geneva has a maximum depth of 1,017 feet; Maggiore, 1,220; and Como, 1,345. Geneva is also of scientific interest, for it was there that the pulsations called "seiches" were first observed. Resembling ocean tides, but quite different in origin, they have been known to cause an abrupt rise of more than five feet at one end of the lake. The north-south movements are more pronounced, but the east-west pulsations also follow a periodic rhythm. They are caused by the effect of variations in atmospheric pressure on confined bodies of water. The deeper the water, and the greater the east-west extension of the body of water, the more pronounced the oscillations are.
Some of Europe's most important rivers bear the melted snows of the Alps to the four points of the compass. Lake Geneva is only a broadening and deepening of the Rhône River, which flows westward to turn south through the vineyards of France and empty into the Mediterranean. The Po, the major Italian river, also fed by Alpine drainage, flows easterly across the plains of Lombardy into the Adriatic. The Rhine, formed by the junction of Alpine streams, descends through winding valleys in a northerly direction to provide a busy avenue of commerce for western Germany, France, and the Low Countries until it empties through a maze of channels into the North Sea. The Danube also levies the Alps for some of its "blue" waters, which eventually reach the distant Black Sea.